Digital photos can have colour filters applied after the fact by software, so are there any good reasons to use colour filters with a digital camera? As I understand it, the main reason for them originally was for effects with black and white film, but now even black and white is a post-processing effect.

I know that UV filters are good for lens protection, and that ND filters allow you to use longer exposures, but what use are colour filters?

8 Answers
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There's a difference between color and color correction filters although they both are colored.

Color correction filters are useful in digital photography to get more even exposure in all channels under some special types of lightning.

For example you'd probably get more exposure and thus less noise in blue channel if you used blue color correction filter (82A/B/C) under tungsten lightning. It should be noted that these filters have filter factor, meaning one stop gain in noise could mean lost stop in terms of exposure time.

In this example two pictures were made in the same conditions under tungsten lightning (street light in winter), the first one shows blue channel from picture without any filtration and the second one blue channel from picture with fairly weak 80D filter. Note the differences in noise. It's important to mention that the white balance reference for both shots was taken from gray card and the blue channel shows more noise in unfiltered case because the blue channel got more amplified in that case.

The usual color filters for BW film are not very useful in digital world as these can easily result overexposure in one channel and leave the other channels underexposed and noisy. Putting a strong color filter in front of your lens means that you are using your digital camera inefficiently, as for example in case of red/blue filter, you're using just 25% of your available pixels and 50% in case of green.

The list of filters with their Wratten number and description can be found from Wikipedia article.

I couldn't figure out how to make pictures link, so drag them to separate tab for 100% view.
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KarelJul 27 '10 at 21:19

two ways: if you're using the new photo-page beta, there should be a "grab the HTML" under the "share this" menu on the photo page, very quick. The more general way via markdown would be this: ![Alt text for screen-readers](jpg URL) -- see photo.stackexchange.com/editing-help
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ex-msJul 27 '10 at 23:38

It should be noted that a filter can only make the image darker, not lighter. By applying a blue filter, you only get more exposure in the blue channel because you darkened the red and green channels, causing you (or the camera's meter) to increase exposure via shutter speed, aperture, or ISO.
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Evan KrallSep 28 '10 at 13:33

Could you re-add the second image? It seems to be gone from Imgur.
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ImreSep 7 '11 at 10:45

With the flexibility offered by digital image programs such as Photoshop, Lightroom, Aperture, and such, there is no reason to use a colored filter on a digital camera. ND filters and polarizers can obtain effects that aren't possible purely through software, but for adding a color cast to an image there's no reason to purchase or carry around a physical filter.

I would say that the biggest advantage of using filters on the camera rather than post-processing in the computer is that you can see the result on the site, making any necessary adjustments. The same goes for in-camera double exposure instead of stacking frames in the computer; you can get immediate feedback on the result.

Keep in mind that color balance of the camera's LCD may be poor, as might the viewing conditions.
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ReidJul 16 '10 at 15:53

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If your camera's LCD color balance is poor and you can't trust it, why are you shooting digital. (Or why don't you get a better camera that you can trust.) Viewing conditions, well that's a good point.
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Jared UpdikeJul 26 '10 at 23:26

You really can't take what the sensor recorded and backwards from there to try to reconstruct the actual wavelengths (or polarization) of the light that went through the lens.

If you could, everyone would be doing IR photography and UV photography without filters at all. The thing is, once you've hit the sensor you've lost some of the information about the light.

Light itself isn't RGB its an entire range of various wavelengths for which the summation of that is something that our eye perceives as color. With a colored filter, you are able to reduce the significance of certain parts of that spectra to either balance out the light (as in the case of correcting for UV light), or remove specific parts of it to achieve a specific purpose.

That remove specific parts is one that you can often see. My favorite is the didymium filter (aka Red Enhancer) which has a transmission spectra that looks like:

That drop at 580nm is around the sodium line (think those yellow street lights) and used for safety glasses for a glass blower so that they can remove the the sodium yellow color in the flame and see the stuff they are working with more clearly.

In photography, the brown fall color leaves aren't brown, they're red, and orange, and yellow and a bunch of other wavelengths. By removing some of the wavelengths near red, the red color comes through more clearly.

You can find similar filters in astrophotography. A 'skyglow' filter to help reduce specific forms of light pollution in the night sky (some use the didymium filter because it cuts out some of the light pollution from a sodium vapor lamp (note that a mercury vapor lamp is much harder to deal with). (see Types of Lamp for more info on this). Alternatively, you might want to just photograph the hydrogen alpha line that only lets in 7nm of bandpass around 656.3nm. Again, these are things that cannot be reconstructed after the fact once the image has been captured.

Gels, and color correcting filters are ones that only allow the light that you want to photograph through to your sensor. Once the entire spectrum of light is collapsed to an RGB value, you cannot pull it apart again to remove specific parts.

Depends why you're using a coloured filter in the first place -- if it's to enhance contrast with a B&W shot, then you may be better with doing this at the digital processing stage (unless you've set the camera to shoot in B&W as JPEG)

If you're wanting to correct or enhance different lighting, you can just fiddle your white balance settings on the camera.

Some artistic effects can be achieved through using coloured filters, but software like Photoshop can emulate all of the settings -- it's just a case of when you want to spend the time -- shooting, or processing

Anything you do at the time you shoot the picture is something you won't do in post-production.

Post-production will always lower picture quality.

Taking that into account what you want to do is maximize the output of your shot and minimize post-processing. That is the rationale behind using filters in digital photography: to maximize quality right out of the shot.

In practice, if you use RAW you will be able to do color filtering with minimal impact.

Why will post-production will always lower picture quality? Or did you just mean if you're shooting JPEG?
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WilkaJul 16 '10 at 15:48

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Why the -1? You always lose quality because you always play with a fixed amount of data. If you shoot RAW and you transform to JPEG you have quality loss already, so it won't affect you. If you use RAW and store the post-processed image in TIFF then you will have quality-loss in comparison with the RAW. I'd even equate this to the conservation of energy. There is no way you can touch something in photoshop and increase quality. The same with optics, anything you put in front will lower quality. It's how the world works.
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RezlajJul 16 '10 at 15:58

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Yeah, I'm not talking about subjective quality. By quality I'm talking of the actual pixel information. Every time you clone, you move the histogram, play with contrast, etc, you are taking a bit out of the overall quality of the image. The question is by what degree do you find it acceptable. What I'm saying is: take a picture using a filter, then take the same picture and apply the filter in post-production, there is NO way those two pictures will have the same quality of information.
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RezlajJul 16 '10 at 18:41

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That's all good and well until you actually want to do something with the changes you've made. Once you get out of raw and actually try to use what you did (like saving as JPEG or TIF to send to the printers) you HAVE TO apply the changes and lose information. If you leave the picture in RAW format then you are right, but I don't know who would do that in the end.
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RezlajJul 26 '10 at 19:52

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This debate is occurring because one side equates "quality" with "information" and the other implicitly recognizes that quality usually has other technical attributes. For instance, sharpening can lose information but enhance quality--even for scientific imaging.
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whuberSep 15 '10 at 15:38